Method for manufacturing golf club head

ABSTRACT

A method for manufacturing a golf club head composed of a metal main body and a non-flat metal face member which are welded each other is disclosed. In order to make the non-flat metal face member, an in-process face material is cut out from a rolled metal plate having a constant thickness. And a turnback is formed around the in-process face material by press working. Before making the press working, the region of the in-process face material corresponding to the turnback is decreased in the thickness by a cutting work.

BACKGROUND OF THE INVENTION

The present invention relates to a method for manufacturing a golf clubhead, more particularly to a method for manufacturing a face memberhaving a turnback from a rolled metal plate.

There has been proposed a hollow golf club head which is, as shown inFIG. 3, composed of a metal main body having a front opening O and anon-flat face member welded thereto, wherein the face member ismanufactured by forging a round bar of the metal material so as to forma turnback, therefore, the face member has a disadvantage such that theproduction cost is high.

SUMMARY OF THE INVENTION

It is therefore, an object of the present invention, to provide a methodfor manufacturing a golf club head in which the non-flat face member isformed from a rolled metal plate at low cost and at a high yield rate.

According to the present invention, a method for manufacturing a golfclub head comprises:

a step of preparing a non-flat metal face member;

a step of preparing a metal head main body; and

a step of welding the non-flat metal face member to the metal head mainbody, wherein

the step of preparing said non-flat metal face member comprises:

a process (a) in which a rolled metal plate having a constant thicknessis prepared;

a process (b) in which an in-process face material is cut out from therolled metal plate after the process (a);

a process (c) in which the face member is prepared by forming theturnback by subjecting the in-process face material to a press workingafter the process (b);

a process (d) in which, in the outer surface of a region correspondingto the turnback (hereinafter, the “corresponding-to-turnback region”),an inclined surface inclined to the inner surface ofcorresponding-to-turnback region towards the peripheral edge ofcorresponding-to-turnback region is formed by a cutting work carried outbefore the process (c) in a state of the in-process face material or ina state of the rolled metal plate so that the thickness of thecorresponding-to-turnback region is continuously decreased towards theperipheral edge of the corresponding-to-turnback region.

DEFINITIONS

In this specification, sizes, positions, directions and the likerelating to the club head refer to those under a standard state of theclub head unless otherwise noted.

Here, the standard state of the club head 1 is such that the club headis set on a horizontal plane HP so that the center line CL of the clubshaft (not shown) is inclined at the lie angle (alpha) while keeping theclub shaft center line CL on a vertical plane, and the club face 2 formsits loft angle with respect to the horizontal plane HP. Incidentally, inthe case of the club head alone, the center line of the shaft insertinghole (h) can be used instead of the center line of the club shaft.

Sweet spot SS is the point of intersection between the club face 2 and astraight line drawn normally to the club face passing the center ofgravity of the head.

Front-back direction is a direction parallel with the above-mentionedstraight line projected on the horizontal plane HP.

Heel-and-toe direction is a direction parallel with the horizontal planeHP and perpendicular to the front-back direction.

Size L of the turnback 9 is a distance in the front-back directionmeasured from the edge (2 a-2 d) of the club face 2 to the rear edge ofthe turnback 9.

If the edge (2 a-2 d) of the club face 2 is unclear due to smooth changein the curvature, as shown in FIGS. 10( a) and 10(b), a virtual edgeline defined based on the curvature change is used instead as follows.In each cutting plane E1, E2—including the sweet spot SS and the centerof gravity of the head, a point at which the radius (r) of curvature ofthe profile line Lf of the face portion first becomes under 200 mm inthe course from the center SS to the periphery of the club face isdetermined. Then, the virtual edge line is defined as a locus of theobtained points.

In the present invention, the face member is obtained by making theturnback by applying press working to the in-process face material cutout from the rolled metal plate, therefore, in comparison with theforging, the face member can be manufactured at low cost.

If a thick rolled metal plate is used in order to secure the durabilityof the face portion, due to the press working, crease and cracks arevery liable to occur on the turnback and consequently the rejection rateof the face member is increased. On the other hand, if a thin rolledmetal plate is used, the pressure molding of the turnback becomes easyand the rejection rate can be improved, but there is a possibility thatthe durability of the face portion becomes insufficient due to the thinmain portion.

In the present invention, in a state of the rolled metal plate or in astate of the in-process face material cut out from the rolled metalplate, the corresponding-to-turnback region is cut into a specificshape. In concrete terms, the thickness of the corresponding-to-turnbackregion is continuously decreased towards its peripheral edge, and theinclined surface inclined to the inner surface towards the peripheraledge is formed in the outer surface of the corresponding-to-turnbackregion. Thereafter, by the press working, the turnback is formed.

According to the present invention, therefore, a thick rolled metalplate can be used to provide a sufficient strength and durability forthe main portion of the face member. Since the corresponding-to-turnbackregion is cut into a specific shape, this region can be deformed easily,therefore, in the press working, the turnback can be bent backward ofthe head largely without causing crease and cracks. In other words, whenthe turnback is formed by pressure molding, a tensile stress occurs inthe outer surface of the corresponding-to-turnback region and acompressive stress occurs in the inner surface, therefore, cracks areespecially liable to occur in the outer surface where a tensile stressoccurs. Further, as the above-mentioned tensile stress is large, theaccuracy of the shape and dimension after bending operation is liable toreduce.

In the present invention, the corresponding-to-turnback regioncontinuously decreases in the thickness towards the peripheral edge andthe inclined surface which inclines to the inner surface towards theperipheral edge is formed in the outer surface thereof. Suchcorresponding-to-turnback region decreases the tensile stress occurringin the outer surface during pressure molding, therefore, cracks whichtend to occur in the outer surface can be effectively prevented, and theworking accuracy and yield rate can be improved.

Accordingly, in the present invention, the non-flat face member can bemanufactured from the rolled metal plate at a high yield rate, and as aresult, the golf club head can be manufactured at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a golf club head according to thepresent invention.

FIG. 2 is a front view thereof.

FIG. 3 is an exploded perspective view thereof.

FIG. 4( a) is a cross sectional view of the face member taken along lineA-A in FIG. 2.

FIG. 4( b) is a cross sectional view of the face member taken along lineB-B in FIG. 2.

FIG. 5 is a perspective view for explaining the rolled metal plate.

FIG. 6( a) is a plan view for explaining a unidirectional rolling.

FIG. 6( b) is a plan view for explaining a multidirectional rolling.

FIG. 7 is a plan view of the rolled metal plate for explaining thecutting-out operation in the process (b).

FIGS. 8( a) and 8(b) are cross sectional views for explaining the pressworking in the process (c).

FIG. 9( a) and FIG. 9( b) are a developed view and a perspective view ofanother example of the face member.

FIG. 10( a) and FIG. 10( b) are a front view and a cross sectional viewof the face portion of a head for explaining the definition of theperipheral edge of the club face,

FIG. 11( a) and FIG. 11( b) are perspective views for explaining theprocess (d).

FIG. 12( a) is a cross sectional view taken along line A-A in FIG. 11(b).

FIG. 12( b) is a cross sectional view taken along line B-B in FIG. 13.

FIG. 12( c) is a partial cross sectional view of the in-process facematerial cut out.

FIG. 13 is a perspective view of the rolled metal plate for explainingthe process (d).

FIG. 14 is a cross sectional view of the corresponding-to-turnbackregion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described in detail inconjunction with accompanying drawings.

In the drawings, golf club head 1 according to the present invention isa hollow head for a wood-type golf club such as driver (#1) or fairwaywood, and the head 1 comprises: a face portion 3 whose front facedefines a club face 2 for striking a ball; a crown portion 4intersecting the club face 2 at the upper edge 2 a thereof; a soleportion 5 intersecting the club face 2 at the lower edge 2 b thereof; aside portion 6 between the crown portion 4 and sole portion 5 whichextends from a toe-side edge 2 c to a heel-side edge 2 d of the clubface 2 through the back face BF of the club head; and a hosel portion 7at the heel side end of the crown to be attached to an end of a clubshaft (not shown) inserted into the shaft inserting hole 7 a. Thus, theclub head 1 is provided with a hollow (i) and a shell structure with thethin wall.

The hollow (i) in this example is a closed void space, but it may befilled with a foamed plastic, separating from the backside of the face3.

In order to improve the directionality of struck balls by increasing themoment of inertia of the head, it is preferable that the volume of thegolf club head 1 is not less than 400 cc, more preferably not less than420 cc, still more preferably not less than 430 cc.

However, if the volume of the club head 1 is too large, the club weightis unfavorably increased, and there is a possibility that the head cannot comply with Golf rules, therefore, it is preferable that the volumeof the golf club head 1 is not more than 470 cc, more preferably notmore than 460 cc.

It is preferable for easy golf swing and swing balance that the mass ofthe golf club head 1 is not less than 180 grams, but not more than 210grams.

In this embodiment, the golf club head 1 is composed of a metal headmain body 1A and a metal face member 1B welded to the main body 1A asshown in FIG. 3.

The face member 1B integrally includes a main portion 8 forming at leasta part of the club face 2 and a turnback 9 extending backward from atleast a part of the edge (2 a-2 d) of the club face 2.

For the face member 1B, for example, stainless steels, maraging steelsand titanium alloys can be used. Especially, titanium alloys having highspecific strength, more specifically titanium alloys having alpha phasesuch as alpha titanium alloys and alpha-beta titanium alloys arepreferably used for the face member 1B.By using an alpha-beta alloy having high specific strength, animprovement in the durability of the face portion 3, a decrease in thethickness of the face member 1B accompanied by a weight reduction, andan increase in the flexibility of designing the center of gravityaccompanying the decreased thickness may be achieved.A typical alpha titanium alloy is Ti-5Al-2.5Sn.Alpha-beta titanium alloys are, for example, Ti-4.5Al-3V-2Fe-2Mo,Ti-4.5Al-2Mo-1.6V-0.5Fe-0.3Si-0.03C, Ti-8Al-1Mo, Ti-1Fe-0.35O-0.01N,Ti-5.5Al-1Fe, Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-2Sn-4Zr-6Mo,Ti-6Al-2Sn-4Zr-2Mo, Ti-8Al-1Mo-1V and the like.Because of the high specific strength and good workability,Ti-4.5Al-3V-2Fe-2Mo, Ti-4.5Al-2Mo-1.6V-0.5Fe-0.3Si-0.03C, Ti-5.5Al-1Feand Ti-8Al-1Mo-1V are preferred.

In this embodiment, the main portion 8 corresponds to the face portion3. In other words, the main portion 8 forms the entirety of the clubface 2, and the main portion 8 forms the entire thickness of the faceportion 3 from the front surface or club face 2 to the rear surface.

Further, the main portion 8 is provided with a thick central region 11,a thin surrounding region 13 having a thickness less than that of thethick central region 11, and an annular transitional region 12 betweenthe regions 11 and 13 whose thickness continuously decreases towards theclub face edge as shown in FIG. 4( a) and FIG. 4( b).

The thick central region 11 has a substantially constant thickness t1which is largest in the face portion 3.

The thick central region 11 includes the sweet spot SS in its center.

The thickness t1 of the thick central region 11 is determined accordingto the metal material used. If the thickness t1 is too small, it becomesdifficult to provide minimum durability necessary for the face portion3. In this light, it is preferable that the thickness t1 of the thickcentral region 11 (namely, the maximum thickness of the face portion 3)is not less than 2.90 mm, more preferably not less than 2.97 mm, stillmore preferably not less than 3.00 mm, most preferably not less than3.05 mm.

If the thickness t1 is too large, the rebound performance tends todeteriorate, causing a decrease in the flying distance of the struckball. In this light, it is preferable that the thickness t1 of the thickcentral region 11 is not more than 3.90 mm, more preferably not morethan 3.85 mm, still more preferably not more than 3.75 mm.

It is preferable that, as shown in FIG. 2, the thick central region 11has a horizontally-long generally-elliptical shape similar to that ofthe club face 2 substantially centered on the sweet spot SS. Therefore,even in the case of average golfers whose ball hitting positions tend tovary wide towards the toe and heel, the ball hitting positions can beeffectively included within the thick central region 11.

The thin surrounding region 13 has a substantially constant thickness t3smallest in the face portion 3, which contributes a weight reduction ofthe face portion 3 and increases the rebound performance of the golfclub head, and the carry distance may be increased.

In this embodiment, the thin surrounding region 13 is formedcontinuously around the thick central region 11.

The thickness t3 of the thin surrounding region may be selecteddepending on the material used.

However, if the thickness t3 is too small, the durability of the faceportion 3 tends to become insufficient, therefore, it is desirable thatthe thickness t3 of the thin surrounding region 13 is not less than 1.50mm, more preferably not less than 1.60 mm, still more preferably notless than 1.65 mm.If the thickness t3 of the thin surrounding region 13 is too large, onthe other hand, the rebound performance deteriorates and there is apossibility that the flying distance of the ball decreases. Therefore,it is preferable that the thickness t3 of the thin surrounding region 13is not more than 2.50 mm, more preferably not more than 2.40 mm, stillmore preferably not more than 2.30 mm.

The transitional region 12 is formed annularly around the thick centralregion 11, and the thickness thereof is continuously decreased towardsthe thin surrounding region 13 in order to improve the durability of theface portion 3.

In this embodiment, the turnback 9 is formed along the entirecircumference of the main portion 8.

As shown in FIG. 3, the turnback 9 includes: a crown-side turnback 9 aextending backward from the upper edge 2 a of the club face 2 to form afront end zone of the crown portion 4; a sole-side turnback 9 bextending backward from the lower edge 2 b of the club face 2 to form afront end zone of the sole portion 5; a toe-side turnback 9 c extendingbackward from the toe-side edge 2 c of the club face 2 to form atoe-side front end zone of the side portion 6; and a heel-side turnback9 d extending backward from the heel-side edge 2 d of the club face 2 toform a heel-side front end zone of the side portion 6.By the turnback 9, the welding position between the face member 1B andhead main body 1A is shifted backward away from the edge of the clubface.

Since the turnback 9 forms the front end zones of the crown portion 4,sole portion 5 and side portion 6, if their maximum thickness t2 isincreased, the rebound performance of the head decreases, and further,cracks and crease are liable to occur during press working. In thislight, it is preferable that the maximum thickness t2 of the turnback 9(excluding the weld bead and the like, if any) is not more than 2.50 mm,more preferably not more than 2.40 mm, still more preferably not morethan 2.30 mm, especially preferably not more than 2.0 mm. If thethickness t2 of the turnback 9 is decrease, the durability of the clubhead is liable to decrease. In this light, it is preferable that thethickness t2 of the turnback 9 is not less than 1.70 mm, more preferablynot less than 1.80 mm, still more preferably not less than 1.85 mm.

The head main body 1A in this embodiment constitutes the part of thegolf club head 1 other than the face member 1B. In other words, the headmain body 1A is made up of: a part 4 a constituting a major aft part ofthe crown portion 4; a part 5 a constituting a major aft part of thesole portion 5; a part 6 a constituting a major aft part of the sideportion 6; and the above-mentioned hosel portion 7, whereby an opening Owhich is closed by the face member 1B is formed at the front of the headmain body 1A.

The head main body 1A is made of a metal material weldable with the facemember 1B. For example, stainless steels, maraging steels, titaniumalloys, aluminum alloys, magnesium alloys and the like can be suitablyused.

As another example of the head main body 1A, for example in order tooptimize the position of the center of gravity of the head, a nonmetalmaterial having a small specific gravity such as fiber reinforced resincan be used in the crown portion, and a weight member having a largespecific gravity can be used in the back of the head, in the soleportion 5 or side portion 6.

A method for manufacturing the above-mentioned golf club head as anembodiment of the present invention is described in detail below.

Firstly, the head main body 1A and the face member 1B are manufactured.

In the case of the head main body 1A in this embodiment which is made ofa single metal material, it is desirable that the head main body 1A isformed as a single casting through a lost-wax precision casting method.

In the case of the face member 1B, it is formed through at least thefollowing processes (a) to (d).

Process (a):

In the process (a), the rolled metal plate M of a constant thickness isprepared.

The rolled metal plate M is a metal plate which is, as shown in FIG. 5,manufactured through a rolling operation, in which the material metal isdragged between oppositely rotating rolls by utilizing the frictiontherebetween and the thickness and sectional area are reduced.The rolled metal plate M means either a unidirectional rolled metalplate M1 which is prepared by rolling repeatedly in one rollingdirection RD as shown in FIG. 6( a), or a multidirectional rolled metalplate M2 which is prepared by rolling repeatedly in at least twodifferent rolling directions including two orthogonal directions RD1 andRD2 as shown in FIG. 6( b).In this embodiment, either a unidirectional rolled metal plate M1 or amultidirectional rolled metal plate M2 can be used for the face member1B.Process (b):In the process (b), an in-process face material 15 for the face memberis prepared. More specifically, after the process (a), an in-processface material 15 is cut out from the rolled metal plate M as shown inFIG. 7.The contour shape of the in-process face material 15 is such that acorresponding-to-main region 16 for forming the main portion 8 and acorresponding-to-turnback region 17 for forming the turnback 9 are atleast included. In other words, the contour shape of the in-process facematerial 15 may be such that it further includes a cutting stock and thelike in its peripheral edge portion.

For example, using a cutting die, a laser cutting machine or the like, alarge number of the in-process face materials 15 can be cut out inmultiple rows and multiple columns from the same rolled metal plate M.

Process (c):

In the process (c), the face member 1B is made.

More specifically, after the process (b), the turnback 9 is formed onthe in-process face material 15 by press working (drawing). Thus, theface member 1B is formed.

As shown in FIGS. 8( a) and 8(b), a press working (drawing) operation iscarried out by the use of paired drawing dies D1 and D2.

One drawing die D2 is provided with a hollow D2 a defining a moldingsurface for molding the club face 2 (namely, front surface) of the facemember 1B. The molding surface is provided with vent holes (V).

The other drawing die D1 is provided with a swell D1 a defining amolding surface for molding the back surface of the club face 2. In thepress working operation, the in-process face material 15 cut out fromthe rolled metal plate M is placed in the hollow D2 a of the femaledrawing die D2 as shown in FIG. 8( a).Then, as shown in FIG. 8( b), the positive drawing die D1 is rammed downtowards the in-process face material 15 in the female drawing die D2,therefore, the corresponding-to-turnback region 17 is bent backward ofthe head, causing a plastic deformation. Thereby, the face member 1Bwith the turnback is manufactured.The press working can be made only one time or plural times on each facematerial 15 as needed.

Since the corresponding-to-turnback region 17 is bent largely duringpress working, as shown in FIG. 9( a) for example, if thecorresponding-to-turnback region 17 is not formed continuously aroundthe corresponding-to-main region 16, namely, if thecorresponding-to-turnback region 17 is formed partially, then, as shownin FIG. 9( b), there is a possibility that, due to the large stressconcentration, the base of the side edges 9E of the turnback 9 causescracks after the press working.

In this embodiment, however, since the corresponding-to-turnback region17 is formed continuously around the main portion 8, such damage can beeffectively prevented.

In the case of a turnback having a large size (L) in the front-backdirection of the head, in order to form such turnback by press working,a large pressure is required, therefore, there is a possibility that theequipment cost and production cost increase. Further, as shown in FIG.3, in the intersecting part j1 between the crown-side turnback 9 a andtoe-side turnback 9 c and also in the intersecting part j2 between thecrown-side turnback 9 a and heel-side turnback 9 d, the amount ofplastic deformation of these parts j1 and j2 during press workingbecomes relatively large and further the deformation is not simple,therefore, damage is especially liable to occur.

Therefore, in the turnback 9 in this embodiment, a large-size part 9Mwhose size (L) in the front-back direction reaches to a maximum value L1is formed in the crown-side turnback 9 a and/or sole-side turnback 9 bwhich are subjected to relatively simple deformation (bendingdeformation) during press working. And the toe-side turnback 9 c andheel-side turnback 9 d include a part whose size L2 in the front-backdirection is not more than 50% of the above-mentioned value L1 of thelarge-size part 9M.

It is especially preferable that the intersecting parts j1 and j2 andthe vicinity thereof have the above-mentioned size L2 of not more than50% of the value L1 of the large-size part. Thereby, it is possible topreserve an appropriate size of the turnback 9 which can preventdeterioration of the rebound performance of the club head 1 andoccurrence of the damage of the turnback 9 during press working.

In the turnback 9 in this embodiment, as shown in FIG. 3, each of thetoe-side turnback 9 a and heel-side turnback 9 b is provided in itsmiddle part in the toe-heel direction with the above-mentionedlarge-size part 9M. And the size L of the turnback is continuouslydecreased towards the toe and heel from the middle part in order toprevent stress concentration during press working and improve theformability.

In this embodiment, the toe-side turnback 9 c and heel-side turnback 9 dare formed continuously so that almost entirety thereof has size of notmore than 50% of the maximum size L1 although it is not always necessaryto have such structure.

In the golf club head 1, if the size L of the turnback 9 is too small,then the weld junction between the face member 1B and head main body 1Aapproaches the edge of the club face, and the rebound performance of theclub head is greatly decreased. In this light, it is preferable that thesize L of the turnback 9 in the front-back direction is not less than3.0 mm, more preferably not less than 5.0 mm, still more preferably notless than 6.0 mm.

If the size L is too large, on the other hand, then the amount oftensile deformation occurring on the outer surface side during pressworking is increased, and cracks and/or crease become liable to occur onthe outer surface. Further, there is a possibility that the shape of theturnback 9 varies due to the difference in the residual stress betweenthe inner surface and outer surface of the turnback 9. Therefore, it ispreferable that the size L of the turnback 9 is preferably not more than13.0 mm, more preferably not more than 11.0 mm, still more preferablynot more than 10.0 mm.Process (d):The process (d) is carried out after the process (a) but before theprocess (c). More specifically, in the state of the in-process facematerial 15 cut out from the rolled metal plate M, OR in the state ofthe rolled metal plate M as shown in FIG. 11, thecorresponding-to-turnback region 17 is cut into a specific shape.In this embodiment, in view of the production efficiency, the process(d) is carried out between process (a) and process (b) in the state ofthe rolled metal plate M.

In the cutting of the corresponding-to-turnback region 17, for exampleas shown in FIGS. 11( a) and 11(b), the rolled metal plate M is fixedonto a bench of a cutting machine (not shown), exposing the innersurface Ma of the rolled metal plate M or the surfaces of thecorresponding-to-turnback region 17 and corresponding-to-main region 16which face the hollow (i) in the finished golf club head, and thethickness of the corresponding-to-turnback region 17 is reduced by theuse of a cutting blade E such as end mill (or face mill).

The cutting work can be carried out with for example a computernumerical controlled three- to five-axis machine having a plurality ofcutting blades. The data used in the cutting work, e.g. cuttingposition, width, depth and the like are programmed beforehand and storedin the computer of the machine

At any rate, the thick central region 11, thin surrounding region 13 andtransitional region 12 are formed in the corresponding-to-main region16.

When the original thickness T of the rolled metal plate M is the same asthe thickness t1 of the thick central region 11, the thick centralregion 11 can be formed without cutting.

By the cutting, the transitional region 12 and thin surrounding region13 are formed around the thick central region 11.

FIG. 12( a) is a cross sectional view taken along line A-A in FIG. 11(b).

By the cutting, the inner surface 17 i of the corresponding-to-turnbackregion 17 is provided with an inclined surface 19. The inclined surface19 in this embodiment is constantly inclined to the outer surface 17 oof the corresponding-to-turnback region 17 toward the peripheral edge17T of the corresponding-to-turnback region 17.After the above-mentioned cutting operation on the inner surfaces of thecorresponding-to-turnback region 17 and corresponding-to-main region 16is done as shown in FIG. 11( b), the rolled metal plate M is turnedinside out to expose its outer surface Mb which becomes the outersurface of the finished golf club head and a cutting operation is madefor the corresponding-to-turnback region 17 as shown in FIG. 13.

FIG. 12( b) is a cross sectional view taken along line B-B in FIG. 13.

In the outer surface 17 o of the corresponding-to-turnback region 17,there is formed an inclined surface 20. The inclined surface 20 isconstantly inclined to the inner surface 17 i of thecorresponding-to-turnback region 17 towards the peripheral edge 17T ofthe corresponding-to-turnback region 17. Therefore, thecorresponding-to-turnback region 17 is tapered, gradually decreasing itsthickness towards the peripheral edge 17T.

Then, the in-process face material 15 is cut out from the rolled metalplate M along the outline of the peripheral edge 17T of thecorresponding-to-turnback region 17, whereby, as shown in FIG. 12( c),the cut-out in-process face material 15 has thecorresponding-to-turnback region 17 whose inner surface 17 i and outersurface 17 o are both machined.

At the time of cut-out, the width Ls of the corresponding-to-turnbackregion 17 is set in a range of about 80 to 100% of the size L of thecorresponding-to-turnback region 17 after subjected to the pressworking.

Here, the expression “continuously decrease” is meant for both of adecrease at a constant rate and a decrease at a variable rate.

As explained, by the cutting work prior to the press working of theprocess (c), the thickness of the corresponding-to-turnback region 17 iscontinuously decreased towards the peripheral edge 17T and the inclinedsurface 20 having a specific shape is formed in the outer surface 17 o,therefore, as shown in FIG. 14, at the time of the press working, theamount of bending of the corresponding-to-turnback region 17 isdecreased, and a tensile stress occurring in the outer surface 17 o canbe mitigated, cracks of the outer surface 90 of the bent turnback 9 canbe effectively prevented, and the forming accuracy of the turnback 9 isincreased to improve the yield rate.

The main portion 8 for hitting a ball has a thickness more than that ofthe corresponding-to-turnback region 17, therefore, a sufficientdurability can be provided.

According to the present invention, the non-flat face member can bemanufactured from the rolled metal plate at a high yield rate, thereforethe golf club head can be manufactured at a low manufacturing cost.

In the above-mentioned embodiment, by the cutting works, the innersurface 17 i and outer surface 17 o of the corresponding-to-turnbackregion 17 are both provided with the inclined surfaces 19 and 20.

The outer surface 17 o should be provided with the inclined surface 20,but it is not always necessary for the inner surface 17 i to form theinclined surface 19 by the cutting work. In this regard, however, inorder to press finish the non-flat face member 1B with high dimensionalaccuracy, it is preferable that the inclined surfaces 19 and 20 areformed in the inner surface 17 i and outer surface 17 o of thecorresponding-to-turnback region 17 as in the above-mentionedembodiment.

As to the configurations of the inclined surfaces 19 and 20, smoothcurve lines can be employed aside from the straight configuration asshown in FIG. 12.

If the thickness t4 of the peripheral edge 17T of thecorresponding-to-turnback region 17 is too small, then due to therepetition of the stress at impact, there is a possibility that cracksoccur at an early stage. If too large on the other hand, there is apossibility that the rebound performance deteriorates and the mass ofthe face member 1B is undesirably increased. In this light, it ispreferable that the thickness t4 is not less than 0.80 mm, morepreferably not less than 0.90 mm, still more preferably not less than0.95 mm, but not more than 1.60 mm, more preferably not more than 1.55mm, still more preferably not more than 1.50 mm.

The thickness of the base 17B of the corresponding-to-turnback region 17is set to be substantially same as the maximum thickness t2 of theturnback 9.

It is preferable that the quotient (t2−t4)/Ls of the difference (t2−t4)between the thickness t2 of the base 17B of thecorresponding-to-turnback region 17 and the thickness t4 of theperipheral edge 17T, divided by the width Ls of thecorresponding-to-turnback region is not less than 0.03, more preferablynot less than 0.05, still more preferably not less than 0.07, but notmore than 0.35, more preferably not more than 0.33, still morepreferably not more than 0.30.If the quotient (t2−t4)/Ls is less than 0.03, the denominator Ls tendsto become large for the numerator (t2−t4). In this case, it becomesdifficult to bend the corresponding-to-turnback region 17 by pressworking, and the product failure and production costs tend to increase.If the quotient (t2−t4)/Ls is more than 0.35, on the other hand, thedenominator Ls tends to become small for the numerator (t2−t4),therefore, the upper limit is preferably 0.35.

For the in-process face material 15 prior to the press working, it ispreferable that the cutting depth d1 of the inclined surface 20 formedon the outer surface 17 o of the corresponding-to-turnback region 17(namely, the maximum depth to the inclined surface as show in FIG. 12(c)) is not less than 0.15 mm, more preferably not less than 0.18 mm,still more preferably not less than 0.20 mm. If the cutting depth d1 isless than 0.15 mm, there is a possibility that the tensile stress of theouter surface of the corresponding-to-turnback region 17 during pressworking can not be well decreased. If the cutting depth d1 is too large,there is a possibility that the strength of thecorresponding-to-turnback region 17 is remarkably decreased. Therefore,it is preferable that the cutting depth d1 is not more than 0.50 mm,more preferably not more than 0.48 mm, still more preferably not morethan 0.45 mm,

It is preferable that the ratio (d1/Ls) of the cutting depth d1 and thewidth Ls of the corresponding-to-turnback region is not less than 0.015,more preferably not less than 0.020, still more preferably not less than0.025.

If the ratio (d1/Ls) is less than 0.015, there is a tendency that thewidth Ls becomes large for the cutting depth d1, and the surface isdamaged during press working. If the ratio (d1/Ls) becomes too large,there is a tendency that the width Ls becomes small for the cuttingdepth d1, therefore, the ratio (d1/Ls) is preferably less than 0.090,more preferably less than 0.085.

In the case that the inclined surface 19 is formed in the inner surface17 i of the corresponding-to-turnback region 17, it is preferable thatthe cutting depth d2 of the inclined surface 19 (namely, the maximumdepth to the inner surface 17 i as shown in FIG. 12( c)) is not lessthan 0.10 mm, more preferably not less than 0.13 mm, still morepreferably not less than 0.15 mm, but not more than 0.30 mm, morepreferably not more than 0.28 mm, still more preferably not more than0.25 mm.

It is preferable that the cutting depth d2 of the inner surface 17 i isless than the cutting depth d1 of the outer surface 17 o.

The ratio (d1/d2) is preferably not less than 2.0, more preferably notless than 2.2, still more preferably not less than 2.5. Thereby, itbecomes possible to bend the corresponding-to-turnback region 17 withhigh dimensional accuracy without causing cracks and crease.

It is preferable that the ratio (d1/d2) is not more than 5.0, morepreferably less than 4.8, still more preferably less than 4.5.

Heretofore, a unidirectional rolled metal plate M1 made of a titaniumalloy having alpha phase has a strength anisotropy such that the tensilestrength Ts1 in the rolling direction RD is smaller than the tensilestrength Ts2 in the direction ND normal to the rolling direction RD.

If the in-process face material has such strength anisotropy and, duringpress working of process (c), it is bent along the rolling direction RDin which direction the tensile strength is lower, damage such as cracksare liable to occur.

Therefore, in the case that a unidirectional rolled metal plate havingsuch a strength anisotropy has to be used, it is necessary to reduce thestrength anisotropy in advance by making a thermal treatment and/oradditional multidirectional rolling which increase the production costs.

In contrast, in the case of the corresponding-to-turnback region 17, thetensile stress occurring in the outer surface 17 o during press workingcan be reduced, therefore, even if the unidirectional rolled metal platehaving the strength anisotropy is used, the above-mentioned damages canbe prevented, and the production costs can be reduced.

As a result, the range of choice for the metal material is widened, andthe production costs can be reduced.

Further, in this embodiment, it becomes possible to provide advantage ofthe durability to the face member 1B by making use of the strengthanisotropy. Specifically, the angle theta between the above-mentionednormal direction ND of the rolled metal plate M and the up-and-downdirection Y of the club face is set to be not more than 45 degrees morepreferably not more than 30 degrees. More specifically, in the process(b), as shown in FIG. 7, in order to meet above-mentioned limitation forthe angle theta, the in-process face material 15 is cut out from therolled metal plate M. As a result, the face portion can be improved inthe durability without increasing the thickness.

In order to derive the above-mentioned advantageous effects, it ispreferable that the rolled metal plate M has such strength anisotropythat the ratio (Ts2/Ts1) of the tensile strength Ts2 in the normaldirection ND to the tensile strength Ts1 in the rolling direction RD isnot less than 1.06, more preferably not less than 1.10, still morepreferably not less than 1.15. But, in order to avoid an excessivedecrease in the tensile strength Ts1 in the rolling direction RD, theratio (Ts2/Ts1) is preferably not more than 1.60, more preferably notmore than 1.50, still more preferably not more than 1.35.

As shown in FIG. 8, the positive drawing die D1 used in the pressworking is provided with a non-flat molding surface corresponding to thethick central region 11, thin surrounding region 13 and transitionalregion 12 of the in-process face material 15. The non-flat moldingsurface can help to accurately position the in-process face material 15relatively to the positive drawing die D1 during press working, and canprevent a possible displacement of the in-process face material 15caused by the pushing-in of the positive drawing die D1. Accordingly,the press working in this embodiment can shape thecorresponding-to-turnback region 17 into the turnback 9 with highdimensional accuracy.

The manufacturing method in this embodiment further includes a processfor giving a bulge and/or roll to the main portion 8 of the face member1B. This process can be incorporated in the press working of the process(c). In this case, the production efficiency can be further improved.Further, this process can be incorporated in the process (b) such thatthe in-process face material 15 is cut out from the rolled metal plate Mby the use of cutting dies provided with a curved surface correspondingto the bulge and/or roll. In this case too, the production efficiencycan be improved. However, it is also possible to carry out the processfor giving a bulge and/or roll as an independent process.

Finally, the face member 1B is welded to the head main body 1A, thus,the golf club head 1 is manufactured.

As to the welding method, Tig welding, plasma welding, laser welding andthe like can be employed. But, soldering may be employed as a kind ofwelding. Especially, the use of laser welding and/or plasma welding ispreferred because the heat-affected zone can be minimized and the jointstrength can be maximized.

Comparison Tests

Wood-type golf club heads having substantially same external forms weremanufactured, using face members having specifications shown in Table 1,and the process yield of each face member was obtained.

The process yield was determined from the results of fifty samples ofeach face member. The larger value is better. When the sample fallenunder the following situations, such sample was rejected: the turnbackwas cracked; the turnback could not be formed; the size of the turnbackdiffered from the design value by 1 mm or more; and the turnback couldnot fit to the front opening of the head main body.

The results are shown in Table 1.

Common specifications are follows:

-   -   head volume: 460 cc    -   loft angle: 11.5 degrees    -   lie angle: 57.5 degrees    -   head main body: lost-wax precision casting of Ti-6Al-4V    -   welding method: plasma welding    -   bulge/roll process: incorporated in the press working in process        (c)    -   normal direction to the rolling direction: at 30 degrees with        respect to the up-and-down direction of the head

TABLE 1 Head Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 7 Ref. 1 Ex. 8 Ref. 2Ref. 3 Face member Rolled metal plate *1 M1 M1 M1 M2 M2 M2 M1 M1 M2 M2Ts2/Ts1 1.15 1.15 1.15 1.21 1.21 1.32 1.15 1.15 1.21 1.32 Order ofprocesses *2 1st cut cut cut cut cut cut cut cut cut cut 2nd CNC CNC CNCCNC CNC CNC CNC CNC CNC CNC inclined surface I&O I&O I&O I&O I&O I&O I OI I 3rd press press press press press press press press press pressWidth of Corresponding- to-turnback region crown-side Ls1 (mm) 10 8 1010 5 10 10 10 10 10 sole-side Ls2 (mm) 10 8 10 10 5 10 10 10 10 10toe-side Ls3 (mm) 5 3 7 5 3 5 5 5 5 5 heel-side Ls4 (mm) 5 5 3 5 3 5 5 55 5 Thickness t1 (mm) 3.28 3.37 3.32 3.45 3.53 3.48 3.33 3.36 3.43 3.50t3 (mm) 1.95 2.05 2.07 2.20 2.27 2.35 2.08 2.11 2.28 2.30 t2(mm) 1.451.40 1.35 1.43 1.38 1.44 1.46 1.49 1.40 1.45 t4(mm) 0.95 1.05 1.02 0.981.05 1.08 1.05 1.02 0.99 1.03 t2 − t4 (mm) 0.50 0.35 0.33 0.45 0.33 0.360.41 0.47 0.41 0.42 Cutting depth d1(mm) 0.35 0.25 0.23 0.36 0.25 0.240.00 0.47 0.00 0.00 d2(mm) 0.15 0.10 0.10 0.09 0.08 0.12 0.41 0.00 0.410.42 (t2 − t4)/Ls1 0.05 0.04 0.03 0.05 0.07 0.04 0.04 0.05 0.04 0.04 (t2− t4)/Ls2 0.05 0.04 0.03 0.05 0.07 0.04 0.04 0.05 0.04 0.04 (t2 −t4)/Ls3 0.10 0.12 0.05 0.09 0.11 0.07 0.08 0.09 0.08 0.08 (t2 − t4)/Ls40.10 0.07 0.11 0.09 0.11 0.07 0.08 0.09 0.08 0.08 d1/Ls1 0.04 0.03 0.020.04 0.05 0.02 0.00 0.05 0.00 0.00 d1/Ls2 0.04 0.03 0.02 0.04 0.05 0.020.00 0.05 0.00 0.00 d1/Ls3 0.07 0.08 0.03 0.07 0.08 0.05 0.00 0.09 0.000.00 d1/Ls4 0.07 0.05 0.08 0.07 0.08 0.05 0.00 0.09 0.00 0.00 d1/d2 2.332.50 2.30 4.00 3.13 2.00 0.00 — 0.00 0.00 Yield rate 100 100 95 98 10096 90 94 88 86 In Table 1: -- *1 Rolled metal plates used are asfollows: M1 - Unidirectional rolled metal plate “TIX51AF” manufacturedby Nippon Steel Corporation whose composition was Ti—5.5Al—1Fe, andthickness was 3.6 mm. M2 - Unidirectional rolled metal plate “Ti-9”manufactured by Kobe Steel, Ltd. whose composition wasTi—4.5Al—2Mo—1.6V—0.5Fe—0.3Si—0.03C, and thickness was 4.0 mm. M3 -Unidirectional rolled metal plate “SP700HM” manufactured by JFE SteelCorporation whose composition was Ti—4.5Al—3V—2Fe—2Mo, and thickness was3.7 mm. *2 Abbreviations in Order of processes are as follows: cut:cutting out of the in-process face material from the rolled metal plateCNC: cutting work by the use of a computer numerical controlled machineI&O: an inclined surface was formed in each of the inner and outersurfaces. I: an inclined surface was formed in the inner surface only.O: an inclined surface was formed in the outer surface only press:pressure molding by the use of the drawing dies D1, D2

From the test results, it was confirmed that, according to the presentinvention, the face members can be manufactured at a high yield rate.

The present invention can be applied to various types of golf club headssuch as iron-type, utility-type and patter-type aside from the wood-typegolf club heads.

1. A method for manufacturing a golf club head comprising: a step ofpreparing a non-flat metal face member which comprises a main portionforming at least a part of a club face for striking a ball and aturnback extending backward from at least a part of the peripheral edgeof the club face; a step of preparing a metal head main body; and a stepof welding the non-flat metal face member to the metal head main body,wherein the step of preparing said non-flat metal face member comprises:a process (a) in which a rolled metal plate having a constant thicknessis prepared; a process (b) in which an in-process face material is cutout from the rolled metal plate after the process (a); a process (c) inwhich the face member is prepared by forming the turnback by subjectingthe in-process face material to a press working after the process (b); aprocess (d) in which, in the outer surface of acorresponding-to-turnback region corresponding to the turnback, aninclined surface inclined to the inner surface ofcorresponding-to-turnback region towards the peripheral edge ofcorresponding-to-turnback region is formed by a cutting work carried outbefore the process (c) in a state of the in-process face material or ina state of the rolled metal plate so that the thickness of thecorresponding-to-turnback region is continuously decreased towards theperipheral edge of the corresponding-to-turnback region.
 2. The methodfor manufacturing a golf club head according to claim 1, wherein theturnback is formed along the entire circumference of the main portion.3. The method for manufacturing a golf club head according to claim 2,wherein the turnback is made up of a crown-side turnback, a sole-sideturnback, a toe-side turnback and a heel-side turnback, and the size ofthe turnback in a front to back direction has a maximum value in thecrown-side turnback and sole-side turnback, and in the toe-side turnbackand heel-side turnback, the size is not more than 50% of said maximumvalue.
 4. The method for manufacturing a golf club head according toclaim 1, 2 or 3, wherein the rolled metal plate having the constantthickness, has a strength anisotropy such that the maximum tensilestrength measured in a certain direction is not less than 1.06 times thetensile strength measured in the normal direction to said certaindirection, and in the process (b), the in-process face material is cutout from the rolled metal plate so that the angle between said certaindirection and the up-and-down direction of the club face becomes notmore than 45 degrees.
 5. The method for manufacturing a golf club headaccording to claim 1, 2 or 3, wherein the rolled metal plate is made ofa titanium alloy having alpha phase, or a stainless steel or a maragingsteel.
 6. The method for manufacturing a golf club head according toclaim 1, wherein the volume of the golf club head is not less than 400cc and not more than 470 cc.
 7. The method for manufacturing a golf clubhead according to claim 1, wherein the mass of the golf club head is notless than 180 grams and not more than 210 grams.
 8. The method formanufacturing a golf club head according to claim 1, wherein the maximumthickness (t2) of the turnback excluding a possible weld bead is notmore than 2.50 mm and not less than 1.70 mm.
 9. The method formanufacturing a golf club head according to claim 1, wherein theturnback is made up of a crown-side turnback, a sole-side turnback, atoe-side turnback and a heel-side turnback, and the size of the turnbackin a front to back direction has a maximum value in the crown-sideturnback and sole-side turnback, and in the intersecting part betweenthe crown-side turnback and toe-side turnback and also in theintersecting part between the crown-side turnback and heel-sideturnback, the size is not more than 50% of said maximum value.
 10. Themethod for manufacturing a golf club head according to claim 1, whereinthe size of the turnback in the front-back direction is not less than3.0 mm and not more than 13.0 mm.
 11. The method for manufacturing agolf club head according to claim 1, wherein the process (d) is carriedout in the state of the rolled metal plate after the process (a) andbefore the process (b).
 12. The method for manufacturing a golf clubhead according to claim 1, wherein by the cutting work in the process(d), each of the inner surface and outer surface of thecorresponding-to-turnback region is provided with the inclined surface.13. The method for manufacturing a golf club head according to claim 1,wherein the thickness (t4) of the peripheral edge portion of thecorresponding-to-turnback region is not less than 0.80 mm and not morethan 1.60 mm.
 14. The method for manufacturing a golf club headaccording to claim 1, wherein the quotient (t2−t4)/(Ls) of thedifference (t2−t4) between the thickness (t2) of thecorresponding-to-turnback region at its the base and the thickness (t4)of the corresponding-to-turnback region at its peripheral edge, dividedby the width (Ls) of the corresponding-to-turnback region is not lessthan 0.03 and not more than 0.35.
 15. The method for manufacturing agolf club head according to claim 1, wherein the cutting depth (d1) ofthe inclined surface formed on the outer surface of thecorresponding-to-turnback region is not less than 0.15 mm and not morethan 0.50 mm.
 16. The method for manufacturing a golf club headaccording to claim 1, wherein the ratio (d1)/(Ls) of the cutting depth(d1) of the inclined surface formed on the outer surface of thecorresponding-to-turnback region to the width (Ls) of thecorresponding-to-turnback region is not less than 0.015 and less than0.090.
 17. The method for manufacturing a golf club head according toclaim 1, wherein the cutting depth of the inclined surface formed on theinner surface of the corresponding-to-turnback region is not less than0.10 mm and not more than 0.30 mm.
 18. The method for manufacturing agolf club head according to claim 1, wherein the cutting depth (d1) ofthe inclined surface formed on the outer surface of thecorresponding-to-turnback region is not less than 0.15 mm and not morethan 0.50 mm, the cutting depth (d2) of the inclined surface formed onthe inner surface of the corresponding-to-turnback region is not lessthan 0.10 mm and not more than 0.30 mm, and the ratio (d1)/(d2) is notless than 2.0 and not more than 5.0.
 19. The method for manufacturing agolf club head according to claim 1, wherein the rolled metal plate is aunidirectionally rolled metal plate.
 20. The method for manufacturing agolf club head according to claim 1, wherein the press working in theprocess (c) is carried out by the use of a pair of drawing dies and,wherein the positive drawing die is provided with a non-flat moldingsurface corresponding to the surface of the thick central region, thinsurrounding region and transitional region of the in-process facematerial.
 21. The method for manufacturing a golf club head according toclaim 1, wherein the step of preparing said non-flat metal face memberfurther comprises: a process for giving a face bulge and/or a face rollto the main portion of the face member which is incorporated in thepress working of the process (c).